Method for refining pig iron into steel

ABSTRACT

A method for refining pig iron containing usual amounts of impurities and elements in a metallurgical vessel into which at least one stream of oxygen is introduced into the body of the pig iron to form at least one reaction zone, and introducing at least one oxide of an element contained in the pig iron in an amount sufficient to saturate the reaction zone with said oxide and thereby promote the oxidation of all other elements contained in the pig iron to the exclusion of the element whose oxide is introduced.

United States Patent [191 Murton METHOD FOR REFINING PIG IRON INTO STEEL[76] Inventor: Crawford B. Murton, 1906 Brushcliff Rd., Pittsburgh, Pa15221 [22] Filed: Nov. 5, 1973 [21] Appl No: 412,563

McClellan 75/59 Josefsson 75/1305 Primary Examinew-L Dewayne RutledgeAssistant Examiner-Peter D. Rosenberg [5 7 ABSTRACT A method forrefining pig iron containing usual amounts of impurities and elements ina metallurgical vessel into which at least one stream of oxygen isintroduced into the body of the pig iron to form at least one reactionzone, and introducing at least one oxide of an element contained in thepig iron in an amount sufficient to saturate the reaction zone with saidoxide and thereby promote the oxidation of all other elements containedin the pig iron to the exclusion of the element whose oxide isintroduced 29 Claims, No Drawings METHOD FOR REFINING PIG IRON INTOSTEEL BACKGROUND OF THE INVENTION 1. Field of the Invention Thisinvention relates to a method for refining molten metal and moreparticularly, it pertains to the refining of pig iron into steel.

2. Description of the Prior Art In the past several methods have beenused for refining molten metal such as steel by the introduction orblowing of air and/or oxygen into the body of molten metal. Thesemethods rely on oxidation reactions with elements and impurities in themolten metal to reduce or eliminate them. Moreover, other compounds suchas steam and/or hydrocarbons have been added to the air or oxygen forvarious reasons including increasing the life of the tuyere by which theair or oxygen is introduced.

The primary disadvantages of the introduction of compounds containinghydrogen into the reaction zone of the metal being refined such as steelis that the resulting steel has an undesirably high content of hydrogen.Moreover, the use of hydrocarbons also introduces additional carbon intothe reaction zone which must ultimately be oxidized by the oxygen toeliminate carbon from the system. In addition, the use of hydrocarbonscontaining sulfur, introduces more sulfur into the reaction zone whichmust ultimately be removed by additional fluxing that requires morerefining time.

ln addition to the foregoing where gases or liquids of hydrocarbons areused to provide a casing of gases or liquids around an oxygen stream toprotect the tuyere from early destruction, an intricate tuyereconstruction is necessary to provide an annular space around the oxygenconduit. Associated with the foregoing is the hazard of explosions Wherefailure of tuyeres of oxygen tube permits intermixing of oxygen andhydrocarbons before reaching the reaction zone. carbonaceous materialbuild up occurs at the mouth of the tuyere which creates safety hazardsor curtails the efficiency of the process.

Furthermore, excessive amounts of hydrocarbons must be used to preservetuyere life in submerged blowing and the conservation of hydrocarbons ismost needed in view of national shortage of capacity to supply thegeneral need for this class of materials.

Associated with the foregoing has been the conventional practice ofoxidizing all of the oxidizable elements contained in the chargematerials. Some of these elements. such as manganese and chromium, aredesirable and valuable. When these valuable metals are oxidized in thecurrent oxygen processes, they are lost in the slag and/or the wastegases.

SUMMARY OF THE INVENTION A method for refining molten metal containingminor amounts of oxiclizable elements in a metallurgical vesselcomprising the steps of introducing at least one stream of oxygenthrough at least one injector into the body of molten metal to form atleast one reaction zone, introducing at least one oxide of theoxidizable elements present in the molten metal to at least one of thereaction zones in amounts sufficient to provide high concentration ofthe oxide or oxides to inhibit or eliminate oxidation of the elements inthe molten metal bath that correspond to said oxide or oxides, andcontinuing to introduce oxygen and oxides until oxidation of the elementin the molten metal of the oxide introduced is reduced or prevented bythe law of mass action.

The advantage of the method of this invention is that it not onlyaccelerates the process of refining the molten metal, but, in addition,such elements as silicon, manganese, and chromium are conserved and areretained in the resulting refined metal. Ferroalloy addi tions may beomitted in most cases. As a result the cost of producing steel islowered significantly.

DESCRIPTION OF THE PREFERRED EMBODIMENT The process for refining moltenmetal of this invention is applicable to the refining of any metal thatis ordinarily refined by oxygen. However, the process is particularlyadaptable to the refining of steei either from pig iron or from someintermediate stage of refinement to the ultimate desired steel analysis.Fig iron contains small amounts of various elements depending uponvarying factors such as the composition of the original ore and suchelements usually include from about 3 to about 4.5% carbon, from aboutU.l5 to about 2.5% manganese, from about 0.5 to about 4.0% silicon, fromabout 0.8 to about 2.0% phosphorus, and from about 0.4 to about l.()%sulfur. Other elements may also be included such as chromium, titanium,molybdenum, nickel, etc.

Moreover, although the method of this invention is particularlyapplicable to those processes where oxygen is introduced into a body oron the surface of the molten-iron-base metal, such as in various formsof the so-called basic oxygen process (BOP), the method may also be usedfor refining steel in an electric furnace, or open hearth furnace, bythe injection of oxides through roof lances or submerged tuyeres.

Generally, the method of this invention is preferably employed for therefining of pig iron into various types of steel, such as steelscontaining various amounts of carbon, manganese, silicon, phosphorus,sulfur, chromium, titanium, molybdenum, nickel, vanadium, boron,columbium, copper, and mixtures thereof.

An example of the method of this invention involves pouring of a desiredamount of molten steel into a basic oxygen converter, commencing to blowat least one stream of oxygen into the body of the molten metal,introducing the necessary amounts of slag-forming materials, such asburnt lime, fluorspar (CaF j or other stag conditioners, introducingwith the steam oxygen particles of the oxide of one or more oxidizableelements present in the molten steel in amounts sufficient to reduce oreliminate oxidation of the element corresponding to the oxide beingreduced, whereby the oxygen input then preferentially oxidizes the otherelements in the metal such as phosphorus, sulfur, and carbon.

All forms of oxides of the oxidizable elements present in the moltenmetal are suitable for the purposes of this invention. When the oxidesare transported by the oxygen stream, the oxides are physically sized toconform to the physical factors required for such transport. Ordinarily,where a regular carbon steel is to be produced, iron oxide is preferablyintroduced with the oxygen stream in order to minimize oxidation of ironduring the refining process. The source of iron oxide to be used is dustof precipitators and collectors of dust resuiting from the refining ofsteel in such furnaces as the open hearth, and the basic oxygenconverter either top blown or bottom blown. Dusts of iron oxide and manganese oxide from collection systems are essential materials forintroduction with oxygen in accordance with this invention.characteristically these dusts have a particle size of about one micron.Sized iron ore or roll scale are further sources of iron oxide. Thisinvention affords the metal industry the opportunity to utilize uselesswaste products of their refining processes to conserve vital rawmaterials, such as iron, manganese, chromium. nickel, by lowering thetotal amount oxidized from the materials charged and further drasticallyreduces the production of these waste products.

For example, when an oxygen stream containing particles of iron oxideand manganese oxide forms a reaction zone in a molten pig iron bath, thepresence of said particles in the reaction zone absorbs heat in theirconversion to the molten state and provides high concentrations ofmolten oxides of iron and manganese in the reaction zone. This divertsthe oxidation reaction between the oxygen stream and the molten pig ironto elements other than iron and manganese. lf particles of silicon oxideand manganese oxide were used, the oxidation of silicon and manganesewould be reduced or preeluded.

Further, if prior to introduction of the oxygen stream the molten bathcontains an excess of an element, such as manganese, in comparison tothe desired analysis of the steel to be produced, the introduction ofthe oxide of manganese is delayed until the excess quantity of manganesein the molten bath has been oxidized and given up to the slag.

Metallic oxides have high heat capacities and absorb heat from reactionzones in their conversion to the mol ten state. The effectivetemperature in the reaction zone is lowered below the vaporizationtemperatures of iron and manganese. Consequently, the emission ofvaporized iron and manganese from the bath is reduced or eliminated bycontrolling the amounts of particulate oxide introduced with the oxygenstream.

In addition, by providing high iron oxide and manga nese oxideconcentrations in the reaction zone the oxidation of other oxidizableelements, such as carbon, is induced and conserves the original amountsof iron and manganese in the molten metal. It is noted in passing thatthe conservation of manganese is vitally important because of its everincreasing scarcity.

When elements other than manganese are to be retained in the moltenbath, the oxides of such elements may be introduced into the oxygenstream either with or without iron oxide. Thus, oxides of such elementsas silicon, phosphorus, sulfur may be added in particulate form, wherebythe elements are retained through the refining process and in theresulting refined steel.

In accordance with this invention, the reaction zone of the molten metalreceive particulates of the oxides of the elements that are to beretained in the refined metal and the oxygen in the oxygen streamoxidizes the other elements. The particulate of the oxides areintroduced into the reaction zone or zones in quantities ranging fromconcentrations sufficient to inhibit oxida tion of the elements desiredto be retained in some cases in quantities sufficient to createsaturation or supersaturation of said zone(s). Those elements to beretained or eliminated comprise any and all of those oxidizable elementsordinarily contained in molten pig iron and any other intermediate gradeof refined steel. The oxides introduced may consist of at least one ofthe elements including iron, carbon, manganese, silicon,

phosphorus, sulfur, chromium, titanium, molybdenum, nickel, vanadium,boron, columbium, copper, and the like. For example, where chromiumexists in the metal to be refined, chromium oxide is introduced into theoxygen stream to prevent oxidation of the chromium in the molten metal.

The following example is illustrative of the present invention:

EXAMPLE A charge of metal consisting of 79 tons of plain carbon steelscrap and of [84 tons of hot metal is charged into a basic oxygenfurnace. The hot metal has a typical composition of 3.4% carbon, l.0%manganese, 0.8% silicon, 1.2% phosphorus, 0.55% sulfur, and the balanceis iron. A lance is introduced into the top of the converter and anoxygen stream at about 180 psi. is directed into the top of the moltencharge. Oxide particles of silicon and manganese having a size of from/2 to 30 microns (preferably 1 micron) are included with the oxygenstream. it is desired to retain about 0.35% silicon and about 0.40%manganese in the refined metal. To achieve this, after 6 minutes ofblowing time 200 lbs/minute of silica is introduced and transported tothe reaction zone to suppress oxidation of silicon in the molten charge.After 8 minutes in addition to the silica input to the oxygen stream,200 lbs/minute of manganese oxide is added to the oxygen stream, or 1.lpounds/minute/ton of pig iron charged. The blow con tinues transportingwith the oxygen steam, the indicated amounts of oxides of silicon andmanganese to the reaction zone until the end of the refining period, orabout 20 minutes from the start of the initial blow. The composition ofthe resulting steel is about 0.1% carbon, 0.40% manganese, 0.35%silicon, 0.022% sulfur, and 0.18% phosphorus.

The cited example indicates a conservation of one ton of manganese andof 0.9 ton of silicon. That is, it was unnecessary to replace silicon ormanganese that would otherwise have been removed from the bath byoxidation in conventional basic oxygen converter prac tice. Moreover,the emission of fine particulate matter from the converter is reduced by38%, because the re action zone temperature is lowered by the oxideintroduction.

Further reduction in particulate emission may be realized byintroduction of iron oxide, which would commence after the tenth minuteof the blow. A useful range of input is from 10 to 2,000 lbs. per minuteof iron oxide (or 0.06 to 1] lbs./minute/ton of pig iron charged) with apreferred range of from about to about 300 lbs. per minute (or 0.9 to1.63 lbs/minutelton). The broad ranges cited reflect the cumulativeeffect of more than one specific oxide being introduced both from achemical and temperature standpoint. However, iron oxide may beintroduced at earlier stages of the oxygen blow either with or withoutoxides to achieve desired final analysis.

in the foregoing example, the useful range of from about 10 to about 600lbs/minute (0.06 to 3.26 lbs./minute/ton of pig iron charged) and apreferred range of from about to about 500 lbs/minute of silicon dioxide(0.6 to 2.72 lbs./minute/ton) may be added. Likewise, the useful rangeof manganese oxide is from about 20 to about i000 lbs/minute (or 0.l lto 5.4 lbs./minute/ton) with a preferred range of from about to about800 lbs/minute (0.95 to 4.35

produced. For that purpose the original charge includl0 ing scrap wouldcontain higher precentages of nickel and chromium. Thereafter, duringthe oxygen blow, oxides of chromium, nickel, and/or other elements areadded in particulate form with the oxygen stream.

Although the preferred procedure for introducing oxides of the elementsset forth above is to introduce those oxides as particulates or powdersthrough a lance with the oxygen stream, the oxides may be introducedinto the reaction zone between the oxygen stream and the molten bathseparately through other conduits or methods. Moreover, where a numberof lances or streams of oxygen and oxides are introduced. the oxygen maybe introduced axially or centrally of the oxides with the oxidesperipherally of the oxygen. On the other hand, the oxides may becentrally or axially disposed with respect to the oxygen.

It is understood that the transport of particulate oxides to thereaction zone may be accomplished in diverse methods. Use of relativelyinert gases such as steam, carbon dioxide, compressed air, argon, fortransport of the oxide particulate and relatively inert gases pluscontrolled amounts of oxygen in a peripheral disposition in relation toa central oxygen stream represent the optimum concept for saidintroduction, but provision of the desired oxide particulate in thereaction zone can be achieved in a variety of ways or combinations.Moreover, the oxides may be introduced in a carrier stream of oxygenwith or without inert gases. Further, the oxygen stream may beintroduced by impinging on the molten bath from the top of the verticalaxis, from the side of the vertical axis, or from the bottom of thevertical axis (submerged).

Accordingly, the method for refining molten metal and preferably steelof this invention provides for the elimination of extraneous sources ofhydrogen into the molten metal, avoid unintentional introduction ofsulfur and prevents the pollution of the atmosphere with 50;, where ironoxide and/or manganese oxide is introduced, increases the yield of ironfrom pig iron from 1.0 to 1.5% by saturating the reaction zone withoxide particles, increases the yield of metallic manganese, avoids theuse of critical energy producing hydrocarbons, and reduces oxygenconsumption because excessive oxidation of iron is prevented anddesirable elements are oxidized only to a desired degree.

What is claimed is:

l. A method of refining molten metal containing oxidizable elements in ametallurgical vessel comprising:

a. blowing an oxygen stream into the molten steel bath of create anoxygen-rich zone therein,

b. then introducing into the oxygen-rich zone a sufficient amount of anoxide of at least one of the oxidizable elements present in the moltenbath in amounts sufficient to provide high concentration of the oxide inthe oxygen-rich zone and thereby to maintain the oxidizable element atthe desired analysis, and

c. continuing to blow oxygen and to introduce said oxide until theanalyses of other oxidizable elements have reached desired analyses.

2. The method of claim 1 further comprising in step a) blowing oxygeninto the molten metal bath until the content of at least one of theoxidizable elements has reached the desired analysis.

3. The method of claim 2 wherein the oxide are introduced in the oxygenstream.

4. The method of claim 1 wherein the oxide are introduced in a separatelance.

5. The method of claim 1 wherein the oxide introduced is selected fromthe group consisting of at least one of the elements including iron,carbon, manganese, silicon, phosphorus, sulfur, chromium, titanium,molybdenum, nickel, vanadium, boron, columbium, copper, and mixturesthereof.

6. The method of claim 1 wherein the oxide are introduced asparticulates in a carrier stream of oxygen.

7. The method of claim 1 wherein the oxide are introduced asparticulates in a carrier stream of a relatively inert gas.

8. The method of claim 1 wherein the oxide are introduced asparticulates in a carrier stream ofa relatively inert gas and oxygen.

9. The method of claim 8 in which one of the oxygen stream and the oxidecarrier stream is introduced in an axially disposed stream and the otherof the oxygen stream and the oxide carrier stream is introduced in aperipherally disposed stream.

10. The method of claim 9 wherein the particulate oxide is introduced ina carrier stream of relatively inert gas peripherally disposed to anoxygen stream.

11. The method of claim 10 wherein oxygen is intro' duced with therelatively inert gas and oxides.

12. The method of claim 11 wherein the oxides are introduced in aperipheral carrier stream of oxygen and the axial stream is oxygen.

13. The method of claim 9 wherein the axial stream is a relatively inertgas with oxides and the peripheral stream is oxygen.

14. The method of claim 13 wherein the axial stream also includesoxygen.

15. The method of claim 1 wherein the molten metal body consistsessentially of pig iron into which silicon dioxide particles areintroduced at a rate of from about 0.06 to about 3.26 lbs/minute/ton ofpig iron charged.

16. The method of claim 15 wherein the silicon dioxide particles areintroduced about 6 minutes after the start of the oxygen blow.

17. The method of claim 15 wherein the silicon dioxide particles areintroduced at a rate of from about 0.6 to about 2.72 lbs/minute/ton.

18. A method of claim 15 wherein the silicon dioxide particles areintroduced at a rate of about l.l lbs/minute/ton.

19. The method of claim 15 wherein manganese oxide particles areintroduced at a rate of from about 20 to about 5.4 lbs./minute/ton withthe silicon oxide.

20. The method of claim 19 wherein the manganese oxide is introducedabout eight minutes after the start of the oxygen blow.

21. The method of claim 19 wherein manganese oxide is introduced at arate of from about 0.95 lbs. to about 4.35 lbs/minute/ton.

22. The method of claim 19 wherein manganese oxide is introduced at arate of about l.l lbs./minute/- ton.

23. The method of claim 1 wherein the oxide introduced is iron oxide.

24. The method of claim 23 wherein iron oxide is introduced at a rate offrom about 0.06 to about ll lbs./minute/ton 25. The method of claim 24wherein iron oxide is introduced at a rate of from about 0.90 to about1.63 lbsjminute/ton 26. The method of claim 20 wherein iron oxide isintroduced at a rate of from 0.06 to about l l lbs./minute/ton abouteight minutes after the start of the oxygen blow.

27. A method of refining molten metal containing oxidizable elements ina metallurgical vessel comprising:

a. introducing at least one stream of oxygen through at least oneinjector into a molten metal bath to form at least one oxygen-rich zone,and

b. introducing at least one oxide of the oxidizable elements present inthe molten metal to at least one of the reaction, zones in amountssufficient to provide high concentration of the oxide and thereby tomaintain the desired analysis of said element or ele ments present inthe molten metal that correspond to the oxides introduced and the timeof said introduction being controlled by the amount of weight percent ofsaid element of elements present in the initial molten metal bath inrelation to the weight percent of said element or elements desiredpresent in the end refined product.

28. The method of claim 6 in which one of the oxy gen stream and theoxide carrier stream is introduced in an axially disposed stream and theother of the oxygen stream and the oxide carrier stream is introduced ina peripherally disposed stream.

29. The method of claim 7 in which one of the oxygen stream and theoxide carrier stream is introduced in an axially disposed stream and theother of the oxygen stream and the oxide carrier stream is introduced ina peripherally disposed stream.

1. A METHOD OF REFINING MOLTEN METAL CONTAINING OXIDIZABLE ELEMENTS IN AMETALLURGICAL VESSEL COMPRISING: A. BLOWING AN OXYGEN STREAM INTO THEMOLTEN STEEL BATH OF CREATE AN OXYGEN-RICH ZONE THEREIN, B. THENINTRODUCING INTO THE OXYGEN-RICH ZONE A SUFFIEIENT AMOUNT OF AN OXIDE OFAT LEAST ONE OF THE OXIDIZABLE ELEMENTS PRESENT IN THE MOLTEN BATH INAMOUNTS SUFFICIENT TO PROVIDE HIGH CONCENTRATION OF THE OXIDE IN THEOXYGENRICH ZONE AND THEREBY TO MAINTAIN THE OXIDIZABLE ELEMENT AT THEDESIRED ANALYSIS, AND C. CONTINUING TO BLOW OXYGEN AND TO INTRODUCE SAIDOXIDE UNTIL THE ANALYSES OF OTHER OXIDIZABLE ELEMENTS HAVE REACHEDDESIRED ANALYSES.
 2. The method of claim 1 further comprising in step a)blowing oxygen into the molten metal bath until the content of at leastone of the oxidizable elements has reached the desired analysis.
 3. Themethod of claim 2 wherein the oxide are introduced in the oxygen stream.4. The method of claim 1 wherein the oxide are introduced in a separatelance.
 5. The method of claim 1 wherein the oxide introduced is selectedfrom the group consisting of at least one of the elements includingiron, carbon, manganese, silicon, phosphorus, sulfur, chromium,titanium, molybdenum, nickel, vanadium, boron, columbium, copper, andmixtures thereof.
 6. The method of claim 1 wherein the oxide areintroduced as particulates in a carrier stream of oxygen.
 7. The methodof claim 1 wherein the oxide are introduced as particulates in a carrierstream of a relatively inert gas.
 8. The method of claim 1 wherein theoxide are introduced as particulates in a carrier stream of a relativelyinert gas and oxygen.
 9. The method of claim 8 in which one of theoxygen stream and the oxide carrier stream is introduced in an axiallydisposed stream and the other of the oxygen stream and the oxide carrierstream is introduced in a peripherally disposed stream.
 10. The methodof claim 9 wherein the particulate oxide is introduced in a carrierstream of relatively inert gas peripherally disposed to an oxygenstream.
 11. The method of claim 10 wherein oxygen is introduced with therelatively inert gas and oxides.
 12. The method of claim 11 wherein theoxides are introduced in a peripheral carrieR stream of oxygen and theaxial stream is oxygen.
 13. The method of claim 9 wherein the axialstream is a relatively inert gas with oxides and the peripheral streamis oxygen.
 14. The method of claim 13 wherein the axial stream alsoincludes oxygen.
 15. The method of claim 1 wherein the molten metal bodyconsists essentially of pig iron into which silicon dioxide particlesare introduced at a rate of from about 0.06 to about 3.26lbs./minute/ton of pig iron charged.
 16. The method of claim 15 whereinthe silicon dioxide particles are introduced about 6 minutes after thestart of the oxygen blow.
 17. The method of claim 15 wherein the silicondioxide particles are introduced at a rate of from about 0.6 to about2.72 lbs./minute/ton.
 18. A method of claim 15 wherein the silicondioxide particles are introduced at a rate of about 1.1 lbs./minute/ton.19. The method of claim 15 wherein manganese oxide particles areintroduced at a rate of from about 20 to about 5.4 lbs./minute/ton withthe silicon oxide.
 20. The method of claim 19 wherein the manganeseoxide is introduced about eight minutes after the start of the oxygenblow.
 21. The method of claim 19 wherein manganese oxide is introducedat a rate of from about 0.95 lbs. to about 4.35 lbs./minute/ton.
 22. Themethod of claim 19 wherein manganese oxide is introduced at a rate ofabout 1.1 lbs./minute/ton.
 23. The method of claim 1 wherein the oxideintroduced is iron oxide.
 24. The method of claim 23 wherein iron oxideis introduced at a rate of from about 0.06 to about 11 lbs./minute/ton25. The method of claim 24 wherein iron oxide is introduced at a rate offrom about 0.90 to about 1.63 lbs./minute/ton.
 26. The method of claim20 wherein iron oxide is introduced at a rate of from 0.06 to about 11lbs./minute/ton about eight minutes after the start of the oxygen blow.27. A method of refining molten metal containing oxidizable elements ina metallurgical vessel comprising: a. introducing at least one stream ofoxygen through at least one injector into a molten metal bath to form atleast one oxygen-rich zone, and b. introducing at least one oxide of theoxidizable elements present in the molten metal to at least one of thereaction, zones in amounts sufficient to provide high concentration ofthe oxide and thereby to maintain the desired analysis of said elementor elements present in the molten metal that correspond to the oxidesintroduced and the time of said introduction being controlled by theamount of weight percent of said element of elements present in theinitial molten metal bath in relation to the weight percent of saidelement or elements desired present in the end refined product.
 28. Themethod of claim 6 in which one of the oxygen stream and the oxidecarrier stream is introduced in an axially disposed stream and the otherof the oxygen stream and the oxide carrier stream is introduced in aperipherally disposed stream.
 29. The method of claim 7 in which one ofthe oxygen stream and the oxide carrier stream is introduced in anaxially disposed stream and the other of the oxygen stream and the oxidecarrier stream is introduced in a peripherally disposed stream.